1. Field of the Invention
The present invention generally relates to a liquid crystal display field, and more particularly to a backlight module and a liquid crystal display.
2. Description of Prior Art
With the population of the liquid crystal display, the demands for the display function of the liquid crystal display are getting higher and higher.
FIGS. 1A and 1B depict partial structure diagrams of a backlight module according to a prior art. Please refer to FIG. 1A. FIG. 1A shows a sectional diagram of the backlight module. As designing the light Emitting Diodes (LEDs) 11 and the light guide plate 12, the coupling efficiency of the lights emitted by the LEDs 11 including the coupling efficiency of the lights progressing from the LEDs 11 to the light guide plate (LGP) 12 has to be considered. Please refer to FIG. 1B. FIG. 1B is a sectional diagram of FIG. 1A. When the distance between the LEDs 11 and the light guide plate 12 is S1, all the lights emitted by the LEDs 11 can enter into the light guide plate 12.
Similarly, the distance perpendicular to the light guide plate 12 from the intersection point of the lights emitted by the adjacent LEDs 11 to the LEDs 11 also needs to be considered. For example, the lights emitted by the LEDs 11 enter the light guide plate 12 are illustrated in FIG. 1A. After the light emitted by one LED 11 enters into the light guide plate 12 and progresses a light coupling distance D1 in the direction B1 perpendicular to the incident side of the light guide plate 12, the light intersects with the light emitted by the adjacent LED 11. Therefore, the lights are emitted by the adjacent LEDs 11 and intersect, a dark area 13 is formed thereby and no light exist in the dark area 13.
Generally, the material of the light guide plate 12 is PMMA (Polymethylmethacrylate). Because the refractive index of the PMMA is larger than the refractive index of the air, the lights will be refracted toward the normal line L after the light emitted by the LED 11 progresses into the light guide plate 12 from the air. That is, the incidence angle θ1 is larger than the departure angle θ2 and the distance D1 (the light coupling distance) in the direction B1 perpendicular to the light guide plate 12 from the intersection point of the lights emitted by the adjacent LEDs 11 to the LEDs 11 becomes larger. Once the light coupling distance D1 becomes large enough to make the dark areas 13 occur in display area 14. The phenomenon of bright and dark mixing display can be happen on the liquid crystal panel.
For shortening the light coupling distance D1 to prevent the occurrence of dark areas 13 in the display area 14, a feasible method is to increase the distance between the LEDs 11 and the light guide plate 12. Please refer to FIG. 2A, the distance between the LEDs 11 and the light guide plate 12 is enlarged as S2 and S2>S1. Although the progressing path of the lights in the direction B1 perpendicular to the light guide plate 12 is longer to decrease the light coupling distance as D2 and D2<D1 to prevent the occurrence of dark areas 13 in the display area 14. However, please refer to FIG. 2B, which is a sectional diagram of FIG. 2A, not all the lights emitted by the LEDs 11 can enter the light guide plate 12. Accordingly, the coupling efficiency of the lights in the direction B1 perpendicular to the light guide plate 12 becomes descended.
In conclusion, it is a research and development aspect of the liquid crystal manufacture skill related with how to shorten a distance perpendicular to the light guide plate from an intersection point of the lights emitted by the adjacent LEDs to the LEDs and prevent the occurrence of dark areas in the display area of the liquid crystal panel as the lights of the LEDs intersect for guaranteeing the display quality of the liquid crystal panel.